Pressure transducers for use in measuring changes in applied mechanical and fluid pressure have been in use for many years. Many such transducers comprise a thin resilient diaphragm which is exposed to a source of pressure to be measured so that deflection of the diaphragm as the pressure changes can be correlated to the magnitude of the actual pressure. The diaphragm typically is linked mechanically with an electro-mechanical transducer such as a strain gage beam.
In some applications where low spring rate is needed or very thin diaphragms are machined integrally with the pressure housing of the transducer, a flat diaphragm may be useful. However, these diaphragms are of limited applicability since their stiffness remains constant only for rather small deflections on the order of a fraction of the thickness of the diaphragm.
To provide improved transducer range or stiffness and yet to retain adequate linearity, preformed convoluted and torus-shaped diaphragms have been used as shown for example, in FIGS. 1 to 3, to be described herein. In some transducers, the preformed diaphragms have been provided with radial flanges for use in welding them between the transducer housing and force transmitting disk or other linkage. Unfortunately, the active portion of diaphragms having such mounting flanges has some frictional contact with the mounting surfaces of the flanges. Thus, movement of the point of contact as the diaphragm flexes causes linearity and hysteresis errors. Since the active portion of the diaphragms is larger on one side than the other, the diaphragm is not symmetric in response to pressure applied from either side. Such asymmetry limits the accuracy of the diaphragm when it is used in differential transducers. To reduce these undesirable effects, prior art transducers have embodied very precisely dimensioned preformed diaphragms which fit closely enough with their support structures to allow deletion of attachment flanges and the use of lap or butt welds at the very edge of the diaphragm between it and the surrounding structure.
To obtain such precisely dimensioned preformed diaphragms, thin, annular metal blanks have been drawn into expensive, very precisely ground dies which impart the desired convoluted or torus-like configuration. Depending on the depth of the convolutions, the spring-back characteristics of the metal and similar factors, maintenance of dimensional control of the finished diaphragm can be quite difficult, resulting in high reject rates and attendant high expense to produce acceptable diaphragms.
Where unflanged diaphragms are used, precise dimensions are needed to ensure that the weld to the housing is hermetic. A very small mismatch between the housing dimensions and the diaphragm dimensions may leave a gap or may cause some crimping of the thin diaphragm at its edges, either of which may be difficult if not impossible to seal by welding. Since leakage past the weld may not be discovered until the assembly is completed, considerable time and money may be lost.